This project involves the continuation of experiments to investigate retrovirus assembly. The site on avian sarcoma virus gag polypeptide p19 to which phospholipid can be cross-linked will be confirmed. Preliminary experiments indicate cross-linking takes place in the N-terminal twenty amino acid residues of the polypeptide. Further properties of a virus assembly mutant that packages uncleaved gag precursor polypeptide will be investigated. The amino acid sequence, location, and role in virion structure of p10 will be determined. A purification of this protein without use of denaturing solvents has been worked out.